Chelmsford County High School for Girls will introduce a new selection system from September to stop middle-class parents subjecting children to up to six years’ worth of coaching in preparation for the admissions test.

Nicole Chapman, the headmistress, said the existing 11-plus “discourages girls whose parents can't afford tutoring” from even applying to the school.

The comments represent the latest in a series of attacks on the private tutoring industry which some experts claim is damaging children’s education by subjecting them to “far too much” pressure at a young age.

One study last year suggested more than half of parents who put sons and daughters through school admissions tests pay for an academic coach or private tutoring company, while thousands more invest in revision books or past papers to give children the edge.

Chelmsford County High – traditionally rated among the top 10 schools in England for GCSE and A-level results – has normally relied on a series of entrance tests set as part of a consortium of grammar schools across Essex.

But the school, which receives around seven applications for every place, is now breaking away from other local schools to run its own “tutor proof” test.

It follows similar moves by schools in Buckinghamshire and the London borough of Bexley.

Council officials in Kent, which has more grammar schools than any other country, are also reviewing the entrance exam sat by local pupils.

Mrs Chapman said: “What we have seen develop across the whole country, not just Essex, is a culture of tutoring and coaching that has reached such high proportions that I have been made aware that it really discourages girls whose parents can’t afford to have tutoring or coaching from even applying.

“On a Saturday morning you can have your child coached while you do your shopping in Sainsbury's.

“I've also heard of little children who are getting up to have coaching before they go to school. No child should be put under this amazing pressure to perform.”

From September, Chelmsford County High will switch to dedicated exams prepared by Durham University’s Centre for Evaluation and Monitoring, which is supposed to distinguish between an average child with coaching and a naturally bright classmate.

It uses less predictable questions and past papers are not available to enable children to revise in advance.

Mrs Chapman added: “Coaching is endemic, absolutely. It leads to social exclusion because parents assume it is a requirement. I have heard it anecdotally that parents say 'oh no, you can't possibly apply because you have to be coached to get in to that school'.

“Some parents start their children at the age of five. They have six years worth of additional training.”